Go to the signature that you want to work on and for this example we are working in adding Microsoft Teams to their Mobile Phone Field:
1st Step is to Highlight the Field that you want to add in the link to Microsoft Teams.
2nd Step is to click on the Link Icon as shown below:
3rd Step is to click the Link Info tab then select the Link Type as URL, Protocol should be selected as <other> and in the URL field type in sip:((Email))
sip:((Email))Click OK to save, to finalize all the revisions click OK again.
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Once saved, and when Recipients of the email clicks on the edited Field it will provide them an option to which program to use.